1. Field of the Invention
The present invention relates to an ignition coil used for generating a spark between a pair of electrodes in a spark plug in an internal combustion engine.
2. Description of Related Art
In an ignition coil used for an internal combustion engine, for example, a primary coil formed by winding a primary wire around a primary spool is disposed concentrically with a secondary coil formed by winding a secondary wire around a secondary spool so as to oppose with each other in a radial direction. A center core made of a magnetic material is disposed on an inner peripheral side of the primary and secondary coils, a peripheral core made of a magnetic material is disposed on the outside of the primary and secondary coils, and a magnetic circuit for generating a magnetic field passing through the center core and the peripheral core is formed.
Clearances in the ignition coil are filled with a filling resin, such as an epoxy resin, to fix and electrically insulate the components. The filling resin is filled in such a manner that the clearances in the ignition coil are evacuated to a vacuum state, and the filling resin in a liquid state is injected into the clearances in the vacuum state and hardened (cured).
However, when defect of the filling resin occurs in the ignition coil, an air gap due to the defect may generate a void (bubble). In a case, where the void moves to a peripheral portion, such as the primary coil or secondary coil, before the filling resin is set, the void may cause a crack or leakage of high-voltage current in the secondary coil. Consequently, various methods for eliminating the factors of checking the injection of the filling resin have been devised.
For example, in an ignition coil disclosed in JP-A-2004-22582, a void passage is provided to vertically penetrate through an upper elastic member, which is disposed above a rod-shaped center core made of a magnetic material, and which is inserted into the inner peripheral side of the primary and secondary coils. A connector, in which an igniter is disposed, is provided with a void passage communicated with the void passage in the upper elastic member. With the above configuration, at the time of charging the epoxy resin into the ignition coil, a void (bubble) existing in a clearance between the center core and an elastic tube covering the center core can be relatively easily released to the outside of the ignition coil via the void passage and the communicated void passage.
In JP-A-2004-22582, however, the communicated void passage has to be formed in a portion where the igniter is disposed in the connector. Thus, it is not easy to form the communicated void passage.
In the technique disclosed in JP-A-2004-22582, the connector has an aligning part for centering (aligning) the center core. In a case, where the aligning part is engaged with an end of the secondary spool on the low-voltage side thereof, it is difficult to sufficiently release a void. Specifically, in JP-A-2004-22582, since the void passage is formed in the upper elastic member, a void generated in the upper elastic member and a void generated in the center portion of the center core can be released. However, a void generated around the periphery of the center core may not be sufficiently released.